Technical Field
Embodiments of the invention relate generally to packaging of devices that are sensitive to temperature, humidity, and/or atmospheric constituents. Particular embodiments relate to packages for micro-electrical-mechanical systems (“MEMS”) that are suitable for use in magnetic-resonance imaging (“MRI”) equipment and in other applications that require non-magnetic components.
Discussion of Art
Micro-electro-mechanical systems (“MEMS”) are devices that have their largest dimension within a range from about 20 micrometers to about 1 millimeter (0.02-1.0 mm). These very small electrical machines are useful in many applications, for example: ejecting ink from the cartridges of inkjet printers to put letters onto a page; measuring accelerations of a vehicle or of a handheld device such as a cellular phone or a game controller; transducing air pressure waves or surface vibrations to record sound; switching optical signals among fiber arrays; etc.
Generally, MEMS are useful for reliably providing highly responsive (small time constant) electromechanical functionality, such as motion sensing, within a small footprint or volume envelope. Accordingly, it has been desired for several years to make use of MEMS for sensing and control within MRI systems. However, it is necessary in MRI systems to provide components that are “non-magnetic,” i.e., neither ferromagnetic nor paramagnetic.
To date, MEMS packaging has relied upon materials that are either ferromagnetic and/or paramagnetic. This has been the case in part because packages fabricated from non-magnetic materials, e.g., ceramics or plastics, have been understood to require closure methods that risked thermal damage, e.g., brazing, and/or chemical damage, e.g., volatile or moisture-permeable adhesives, to the MEMS enclosed within the packages. MEMs are sensitive to their environment, particulate or chemically, and also are sensitive to the packaging processing conditions, thus the need for a process to control the conditions and package environment. Indeed, MEMS typify a category of “sensitive” components that require special care in packaging. Other constituents of this category may include piezoelectric, paramagnetic, and shape memory alloy devices.
In view of the above, it is desirable to provide a sensitive component within a non-magnetic hermetic package. A key difficulty in providing such a package has been to devise a method of bonding a sensitive component into an open non-magnetic package cavity, then sealing the package cavity, without inducing thermal and/or chemical damage to the sensitive component.